1. Field of the Invention
The present invention relates to a messaging system for passing messages between calling programs and called programs, and in particular to a messaging system wherein all messages are passed within a defined message block, and via a message interface.
2. Related Art
Large computer systems generally comprise a number of components, or programs which interact with each other via calls. Dividing a large computer system into a number of programs is advantageous for many reasons, for example, it enables a number of computer programmers to work on the system with some degree of independence, it allows the computer system to be modified or enhanced more easily, and it allows the programs within the system to be reused in other computer systems.
The interface between the various programs within a computer system must be defined, so that a calling program is able to call a called program. In known computer systems the interface between programs is embodied in the computer code of both the calling and the called programs, thus if one calling program within a computer system is altered so as to require a change to the interface, all other programs calling the altered program must also be altered to conform to the new interface requirements.
A system which provides an interface between applications and various computers attached to a computer network is described in European Patent Application EP-A-0 414 624.
A further problem arises when, for example due to the growth of the computer system, a program needs to be moved from the initial physical hardware e.g. a mainframe, to another physical system, the interface must be enhanced to allow this. This enhancement must be made to all calling programs still resident on the initial mainframe, in addition to those programs which have been moved to the remote physical system.